The present invention relates to a magnetic head for reproducing information recorded at high density and a method of producing the magnetic head, and a magnetic recording and reproducing apparatus comprising the magnetic head, as well as a perpendicular magnetic recording medium, such as a video disc or a hard disk, and a method of producing the medium.
A magnetic recording and reproducing apparatus is available in various types, such as a tape recorder, a video tape recorder and a magnetic disc apparatus. The magnetic recording and reproducing apparatus is evolving so as to carry out high-density recording and have been improved in many ways to achieve the purpose. These improvements are: a track is made narrower by using a narrower head; a plurality of magnetic heads are used; a recording medium is made smoother and thinner; the relative speed between the magnetic head and the recording medium is increased; and so on.
Accordingly, there is a need for a magnetic head capable of recording information on a magnetic recording medium at high density and also capable of reproducing the information. To meet such a need, a complex MR head comprising an MR (magneto-resistance) head, which is a reproduction-only head having a higher reproduction sensitivity than that of a widely used induction type head, has become commercially available. The complex MR head is provided with both the MR head and a conventional induction thin-film head. The MR head having high reproduction sensitivity is used in reproduction, and the conventional induction thin film head is used in recording. The MR head comprises a magneto-resistance effect device (hereinafter referred to as an MR device). However, the structure of the complex MR head comprising the MR device is more complicated than that of a conventional induction head. More specifically, a shielding layer is required around the MR device, and a magnetic gap is required for reproduction. Furthermore, it is necessary to have a structure for arranging an MR film so that the MR film can have a single magnetic domain, and it is also necessary to have a unique structure for applying a bias magnetic field for linear reproduction.
For these reasons, advanced production technology is required for producing the complex MR head, thereby making it difficult to attain high yield.
Longitudinal recording, wherein magnetization is performed in the direction parallel to the track of a recording medium, has been used as a recording method for a conventional magnetic recording and reproducing apparatus. However, in the case of the longitudinal recording, micro magnetic domains magnetized in the direction parallel to the surface of a recording film repels adjacent magnetic domains, and they tend to mutually weaken magnetization. This tendency becomes more significant as recording density is higher, thereby causing a limitation in high-density recording.
Perpendicular magnetic recording, wherein magnetization is performed in the direction perpendicular to the surface of a recording medium, is available as a method of solving the above-mentioned problem. A perpendicular magnetic recording median having a two-layer structure has been commercially available as a recording medium for performing recording in accordance with perpendicular magnetic recording. In the perpendicular magnetic recording medium, a soft magnetic film having a high permeability is used as a foundation layer. A perpendicular recording film having an axis of easy magnetization in the direction perpendicular to the surface of the soft magnetic film is laminated on the foundation layer. The soft magnetic film is made of a nickel-iron alloy (Ni--Fe) or the like, and the perpendicular recording film is made of a cobalt-chromium alloy (Co--Cr) or the like. These films are formed by sputtering or the like. When these films are formed, it is desired that the soft magnetic film and the perpendicular recording film are continuously formed in a vacuum chamber so as to prevent contamination caused by entry of dust or by formation of oxidized films between the soft magnetic film used as the foundation layer and the perpendicular recording film. In this case, the sputtering process is conducted while the substrate of a recording medium passes over two kinds of target materials in sequence at a predetermined speed.
The soft magnetic film, namely, the foundation layer, allows the recording magnetic field from the perpendicular magnetic head for perpendicularly magnetizing the perpendicular recording film to pass in the longitudinal direction parallel to the surface of the recording medium and to return to the perpendicular magnetic head. In addition, the soft magnetic film has a role to enhance the efficiency of magnetic field generation in record and reproduction. Therefore, controlling the anisotropy of the soft magnetic film is important to enhance record and reproduction characteristics. In other words, it is necessary to align the axis of hard magnetization, which is orthogonal to the axis of easy magnetization of the soft magnetic film, in the traveling direction of the substrate in record and reproduction. In the case of a magnetic disc, it is necessary to align the axis of hard magnetization of the soft magnetic film in the direction parallel to the circumference of the disc, since a recording track is formed in the direction along the circumference thereof.
A method of forming a soft magnetic film by controlling the angle between the target material and the substrate and a method of forming a soft magnetic film by applying a magnetic field have been proposed as control methods of the anisotropy of the soft magnetic film. Furthermore, a method of applying a magnetic field after the soft magnetic film was formed and before the perpendicular recording film is formed has also been proposed (Japanese Laid-open Patent Application Hei 5-258274). A method of applying a magnetic field in the radial direction of the magnetic disc has been proposed as a method of aligning the axis of hard magnetization of the soft magnetic film in the direction parallel to the circumference of the magnetic disc. In all these methods, processing is carried out before or while the perpendicular recording film is formed.
When a magnetic field is applied to a perpendicular magnetic recording medium in a vacuum, difficult problems are caused in handling; for example, a complicated mechanism must be provided and operated in a vacuum sputtering apparatus. For easier handling, it is desired that a magnetic field is applied by using an apparatus which is separate from the sputtering apparatus and provided in the atmosphere. However, since it is desired that the soft magnetic film and the perpendicular recording film are continuously formed in a vacuum as described above, sputtering is performed by passing the substrate over two target materials in a vacuum at a predetermined speed.
In a currently available sputtering apparatus, however, in order to apply the magnetic field to the magnetic disc in the radius direction before forming of the perpendicular recording film, the sputtering process must be interrupted once after the soft magnetic film is formed, and the perpendicular magnetic recording medium must be taken out to the atmosphere. In case the continuity of the film forming process is lost as described above, there is the danger of contaminating the recording medium because of entry of dust or formation of oxidized films between the foundation layer and the perpendicular recording film. Besides, sputtering must be performed twice for the foundation layer and the perpendicular recording film layer, thereby increasing the number of steps, lowering productivity, and increasing production cost.
Other problems encountered in high-density record and reproduction are caused by tracking control methods. According to one of the methods, in order to perform tracking control for a predetermined track of a magnetic disc, markers are formed on the recording medium by a physical process using etching or the like, and servo control is activated by using laser beams reflected from the markers. As a method of placing the markers, pits and projections are formed by processing the surface of the medium by a physical process such as photolithography or the like. However, this method causes high production cost. Furthermore, in the case that the method is used for hard disk drives (HDD), the floating condition of the head is changed by the pits and projections in high-density recording, and the head might be damaged in an extraordinary case.